Eyes throb in bright sun after days in dark -- Why?

Clearly this is a useful defense mechanism but I’m wondering:

  1. If I’m in the dark all night, bright sun in the morning doesn’t hurt. So why does a prolonged period of darkness followed by intense light cause that throbbing pain in the eyes?

  2. What is the actual mechanism is triggering the pain?

well IANAO (optometrist), but i would imagine that the pain is from the fast reflex experienced by your cornea, which contracts when confronted by bright light to protect the cornea. if you go from complete darkness to bright light, your cornea wishes it could cover the pupil completely, but it can’t, so it hurts when it is trying to do so.

i get up before sunrise every morning (except weekends), so i wouldn’t know the feeling. but my eyes hurt even when i turn on the light in the bathroom in the morning. but when i wake up on the weekends, my bedroom has gradually filled with sunlight, adjusting my eyes to the light even through my eyelids (and i’m also known to sleep with my eyes open–i know, i’m a freak).

dammit–pupil, the cornea protects the pupil. i would ask a mod to change it but i know it wouldn’t happen without some sort of bribe being involved.